What disinfects water in the tap. Disinfection of water in the field. Other halogens for water disinfection
Plan
Introduction.
1. Hygienic problems of drinking water disinfection.
2. Reagent (chemical) methods of drinking water disinfection.
2.1 Chlorination.
2.1.2 Chlorine dioxide.
2.1.3 Sodium hypochlorite.
2.2 Ozonation.
2.3 Other reagent methods of water disinfection.
3. Physical methods of drinking water disinfection.
3.1 Boiling.
3.2 Ultraviolet irradiation.
3.3 Electropulse method.
3.4 Ultrasonic disinfection.
3.5 Radiation disinfection.
3.6 Other physical methods.
4. Complex disinfection.
Conclusion.
Bibliography.
Introduction
Among the many branches of modern technology aimed at improving the standard of living of people, the improvement of populated areas and the development of industry, water supply occupies a large and honorable place. After all, water is an indispensable part of all living organisms, the vital activity of which is impossible without water. For normal flow physiological processes in the human body and to create favorable living conditions for people, the hygienic value of water is very important. At present, providing the population with high quality water has become a real problem.
The problem of drinking water supply affects many aspects of the life of human society throughout the history of its existence. At present, this is a social, political, medical, geographical, as well as engineering and economic problem. About 5-6% of the total water consumption is spent on drinking and domestic needs of the population, communal facilities, medical institutions, as well as on the technological needs of food industry enterprises. Technically, it is not difficult to supply such an amount of water, but the needs must be satisfied with water of a certain quality, the so-called drinking water.
Drinking water is water that meets the established regulatory requirements in terms of its quality in its natural state or after treatment (purification, disinfection) and is intended for drinking and domestic needs of a person. Basic requirements for the quality of drinking water: to be safe in epidemic and radiation terms, to be harmless in chemical composition, to have favorable organoleptic properties. To meet these requirements, a whole range of measures for the preparation of drinking water is currently used.
Of course, in rivers and other bodies of water there is a natural process of water self-purification. However, it proceeds very slowly. Rivers have long been unable to cope with wastewater discharges and other sources of pollution. But the level of bactericidal effects in wastewater often exceeds the norm by thousands and millions of times. Effluent enters rivers and lakes, and most city water utilities take their water from them. Thus, the mandatory processes in the preparation of drinking water are high-quality purification and disinfection of wastewater.
Disinfection of water is the process of destroying microorganisms present there. In the process of primary water treatment, up to 98% of bacteria are retained. But among the remaining bacteria, as well as among viruses, there may be pathogenic (disease-causing) microbes, for the destruction of which special water treatment is needed - its disinfection.
With the complete purification of surface waters, disinfection is always necessary, and when using groundwater– only when the microbiological properties of the source water require it. But in practice, the use of both groundwater and surface water for drinking is almost always impossible without disinfection.
1.Hygienic tasks of drinking water disinfection
The water of natural sources of drinking water supply, as a rule, does not meet the hygienic requirements for drinking water and requires preparation before being supplied to the population - cleaning and disinfection.
Water purification, including its clarification and discoloration, is the first stage in the preparation of drinking water. As a result, suspended solids, helminth eggs and a significant part of microorganisms are removed from the water. But some pathogenic bacteria and viruses penetrate through treatment facilities and are contained in filtered water. To create a reliable and manageable barrier to the possible transmission of intestinal infections and other equally dangerous diseases through water, water disinfection is used, i.e. destruction of living and virulent pathogenic microorganisms - bacteria and viruses. After all, it is the microbiological contamination of water that occupies the first place in assessing the degree of risk to human health. Today it has been proven that the risk of diseases from pathogenic microorganisms present in water is thousands of times higher than when water is polluted with chemical compounds of various nature. Therefore, disinfection to the limits that meet the established hygienic standards is a prerequisite for obtaining drinking water.
In the practice of municipal water supply, reagent (chlorination, ozonation, exposure to silver preparations), non-reagent (ultraviolet rays, exposure to pulsed electrical discharges, gamma rays, etc.) and combined methods of water disinfection are used. In the first case, the desired effect is achieved by introducing biologically active chemical compounds into the water. Reagent-free disinfection methods involve the treatment of water by physical influences. And in combined methods, chemical and physical effects are used simultaneously.
When choosing a method of disinfection, one should take into account the danger to human health of residual amounts of biologically active substances used for disinfection or formed in the process of disinfection, the possibility of changing the physicochemical properties of water (for example, the formation of free radicals). Important characteristics of the disinfection method are also its effectiveness in relation to various types of water micropopulation, the dependence of the effect on environmental conditions.
With chemical methods of drinking water disinfection, in order to achieve a stable disinfecting effect, it is necessary to correctly determine the dose of the injected reagent and ensure a sufficient duration of its contact with water. The dose of the reagent is determined by trial disinfection or calculation methods. To maintain the desired effect in chemical methods of drinking water disinfection, the dose of the reagent is calculated with an excess (residual chlorine, residual ozone), which guarantees the destruction of microorganisms that enter the water for some time after disinfection.
With physical methods, it is necessary to bring to a unit volume of water a given amount of energy, defined as the product of the intensity of exposure (radiation power) by the contact time.
There are other restrictions in the use of one or another method of water disinfection. These limitations, as well as the advantages and disadvantages of disinfection methods, will be discussed in detail below.
2.Reagent (chemical) methods of drinking water disinfection
2.1 Chlorination
The most common and proven method of water disinfection is primary chlorination. Currently, 98.6% of water is disinfected by this method. The reason for this is the increased efficiency of water disinfection and the efficiency of the technological process in comparison with other existing methods. Chlorination allows not only to purify water from unwanted organic and biological impurities, but also to completely remove dissolved salts of iron and manganese. Another major advantage of this method is its ability to ensure the microbiological safety of water during its transportation to the user due to the aftereffect.
A significant disadvantage of chlorination is the presence of free chlorine in the treated water, which worsens its organoleptic properties and causes the formation of side halogen-containing compounds (HCC). Most of the GSS are trihalomethanes (THM) - chloroform, dichlorobromomethane, dibromochloromethane and bromoform. Their formation is due to the interaction of active chlorine compounds with organic matter natural origin. This process is extended in time up to several tens of hours, and the amount of THM formed, other things being equal, is the greater, the higher the pH of the water. To eliminate impurities, additional purification of water on coal filters is required. Currently, the maximum allowable concentrations for substances that are by-products of chlorination are set in various developed countries in the range from 0.06 to 0.2 mg/l and correspond to modern scientific ideas about the degree of their danger to health.
For chlorination of water, substances such as chlorine itself (liquid or gaseous), chlorine dioxide and other chlorine-containing substances are used.
2.1.1 Chlorine
Chlorine is the most common of all substances used to disinfect drinking water. This is due to the high efficiency, simplicity of the technological equipment used, the low cost of the reagent used - liquid or gaseous chlorine - and the relative ease of maintenance.
A very important and valuable quality of using chlorine is its aftereffect. If the amount of chlorine is taken with some calculated excess, so that after passing through the treatment plant, the water contains 0.3–0.5 mg / l of residual chlorine, then there is no secondary growth of microorganisms in the water.
However, chlorine is a potent toxic substance requiring special safety measures during its transportation, storage and use; measures to prevent catastrophic consequences in emergency situations. Therefore, there is a constant search for reagents that combine the positive qualities of chlorine and do not have its disadvantages.
Simultaneously with water disinfection, oxidation reactions of organic compounds occur, in which organochlorine compounds are formed in water, which are highly toxic, mutagenic and carcinogenic. Subsequent purification of water on active carbon cannot always remove these compounds. In addition to becoming a contaminant of drinking water, these highly persistent organochlorine compounds, when they pass through the water supply and sewage system, cause pollution of downstream rivers.
The presence of side compounds in water is one of the disadvantages of using gaseous as well as liquid chlorine (Cl2) as a disinfectant.
2.1.2 Chlorine dioxide
Currently, the use of chlorine dioxide (ClO 2 ) is also proposed for the disinfection of drinking water, which has a number of advantages, such as: a higher bactericidal and deodorizing effect, the absence of organochlorine compounds in the treatment products, an improvement in the organoleptic qualities of water, and the absence of the need to transport liquid chlorine. However, chlorine dioxide is expensive and must be produced locally using rather complex technology. Its application is promising for installations of relatively small productivity.
The effect of ClO2 on the pathogenic flora is due not only to the high content of released chlorine during the reaction, but also to the resulting atomic oxygen. It is this combination that makes chlorine dioxide a stronger disinfectant. In addition, it does not impair the taste and smell of water. The limiting factor in the use of this disinfectant until recently was the increased explosiveness, which complicated its production, transportation and storage. However modern technologies make it possible to eliminate this disadvantage by producing chlorine dioxide directly at the point of use.
Description of the presentation on individual slides:
1 slide
Description of the slide:
2 slide
Description of the slide:
Methods: Chlorination Chlorine Chlorine dioxide Sodium hypochlorite Chlorine-containing preparations Ozonation Other reagent methods of water disinfection Boiling Ultraviolet radiation Electropulse method Ultrasonic disinfection Radiation disinfection
3 slide
Description of the slide:
Chlorination The most common and proven method of water disinfection is primary chlorination. Currently, 98.6% of water is disinfected by this method. The reason for this is the increased efficiency of water disinfection and the efficiency of the technological process in comparison with other existing methods. Chlorination allows not only to purify water from unwanted organic and biological impurities, but also to completely remove dissolved salts of iron and manganese. Another major advantage of this method is its ability to ensure the microbiological safety of water during its transportation to the user due to the aftereffect. For chlorination of water, substances such as chlorine itself (liquid or gaseous), chlorine dioxide and other chlorine-containing substances are used.
4 slide
Description of the slide:
Chlorine Chlorine is the most common of all substances used to disinfect drinking water. This is due to the high efficiency, simplicity of the technological equipment used, the low cost of the reagent used - liquid or gaseous chlorine - and the relative ease of maintenance. A very important and valuable quality of using chlorine is its aftereffect. If the amount of chlorine is taken with some calculated excess, so that after passing through the treatment plant, the water contains 0.3–0.5 mg / l of residual chlorine, then there is no secondary growth of microorganisms in the water. The presence of side compounds in water is one of the disadvantages of using gaseous as well as liquid chlorine (Cl2) as a disinfectant.
5 slide
Description of the slide:
Chlorine dioxide At present, the use of chlorine dioxide (ClO2) is also proposed for the disinfection of drinking water, which has several advantages, such as: higher bactericidal and deodorizing effect, absence of organochlorine compounds in the treatment products, improved organoleptic qualities of water, no need to transport liquid chlorine . However, chlorine dioxide is expensive and must be produced locally using rather complex technology. Its application is promising for installations of relatively small productivity.
6 slide
Description of the slide:
Sodium hypochlorite Sodium hypochlorite (NaClO) technology is based on its ability to decompose in water to form chlorine dioxide. The use of concentrated sodium hypochlorite reduces secondary pollution by a third compared to the use of gaseous chlorine. In addition, the transportation and storage of a concentrated NaClO solution is quite simple and does not require increased security measures. It is also possible to obtain sodium hypochlorite directly on site, by electrolysis. The electrolytic method is characterized by low costs and safety; the reagent is easily dosed, which allows you to automate the process of water disinfection.
7 slide
Description of the slide:
Chlorine-containing preparations The use of chlorine-containing reagents (bleach, sodium and calcium hypochlorites) for water disinfection is less dangerous to maintain and does not require complex technological solutions. True, the reagent economy used in this case is more cumbersome, which is associated with the need to store large quantities of preparations (3–5 times more than when using chlorine). The volume of traffic increases by the same amount. During storage, partial decomposition of the reagents occurs with a decrease in the chlorine content. There is still a need to install an exhaust ventilation system and observe safety measures for maintenance personnel. Solutions of chlorine-containing reagents are corrosive and require equipment and pipelines made of stainless materials or with an anti-corrosion coating.
8 slide
Description of the slide:
Ozonation The advantage of ozone (O3) over other disinfectants lies in its inherent disinfecting and oxidizing properties, due to the release of active atomic oxygen upon contact with organic objects, which destroys the enzyme systems of microbial cells and oxidizes some compounds that give water an unpleasant odor (for example, humic bases) . In addition to the unique ability to kill bacteria, ozone is highly effective in killing spores, cysts and many other pathogenic microbes. Historically, the use of ozone began as early as 1898 in France, where pilot plants for the preparation of drinking water were first created. From a hygienic point of view, water ozonation is one of the better ways disinfection of drinking water. At high degree disinfection of water, it provides its best organoleptic characteristics and the absence of highly toxic and carcinogenic products in purified water. The method of water ozonation is technically complex and the most expensive among other methods of drinking water disinfection. . All this limits the use of this method in everyday life.
9 slide
Description of the slide:
Other reagent methods of water disinfection The use of heavy metals (copper, silver, etc.) for the disinfection of drinking water is based on the use of their "oligodynamic" properties - the ability to have a bactericidal effect in low concentrations. These metals can be introduced in the form of salt solutions or by electrochemical dissolution. In both these cases, indirect control of their content in water is possible. It should be noted that MPCs of silver and copper ions in drinking water are quite strict, and the requirements for water discharged into fishery reservoirs are even higher. Chemical methods for the disinfection of drinking water also include widely used in the early 20th century. disinfection with bromine and iodine compounds, which have more pronounced bactericidal properties than chlorine, but require more sophisticated technology. In modern practice, for the disinfection of drinking water by iodization, it is proposed to use special ion exchangers saturated with iodine. When water is passed through them, iodine is gradually washed out of the ion exchanger, providing the necessary dose in water. This solution is acceptable for small-sized individual installations. A significant disadvantage is the change in the concentration of iodine during operation and the lack of constant monitoring of its concentration.
10 slide
Description of the slide:
The use of active carbons and cation exchangers saturated with silver, for example, C-100 Ag or C-150 Ag from Purolite, does not aim to “silver” the water, but to prevent the development of microorganisms when the flow of water stops. When stopping, ideal conditions are created for their reproduction - a large amount of organic matter retained on the surface of the particles, their huge area and elevated temperature. The presence of silver in the structure of these particles dramatically reduces the likelihood of contamination of the loading layer. Silver-containing cation exchangers developed by OAO NIIPM - KU-23SM and KU-23SP - contain a much larger amount of silver and are designed for water disinfection in small-capacity installations.
11 slide
Description of the slide:
Boiling Of the physical methods of water disinfection, the most common and reliable (in particular, at home) is boiling. Boiling destroys most bacteria, viruses, bacteriophages, antibiotics and other biological objects, which are often found in open water sources, and as a result, in central water supply systems. In addition, when water is boiled, gases dissolved in it are removed and hardness decreases. The taste qualities of water during boiling change little. True, for reliable disinfection, it is recommended to boil water for 15 - 20 minutes, because. during short-term boiling, some microorganisms, their spores, helminth eggs can remain viable (especially if microorganisms are adsorbed on solid particles). However, the use of boiling on an industrial scale, of course, is not possible due to the high cost of the method.
12 slide
Description of the slide:
Ultraviolet Radiation UV treatment is a promising industrial method for water disinfection. In this case, light with a wavelength of 254 nm (or close to it), which is called bactericidal, is used. The disinfecting properties of such light are due to their action on cellular metabolism and especially on the enzyme systems of the bacterial cell. At the same time, bactericidal light destroys not only vegetative, but also spore forms of bacteria. This method is acceptable both as an alternative and as an addition to traditional disinfectants, since it is absolutely safe and effective.
13 slide
Description of the slide:
Electropulse method A fairly new method of water disinfection is the electropulse method - the use of impulsive electrical discharges (IED). The technological process consists of six stages: 1) supplying liquid to the working volume with a uniform velocity distribution profile (moreover, the working volume is filled with an air gap, and a uniform liquid distribution profile helps to reduce the energy intensity of the process) 2) charging the energy storage device in constant power mode 3) initiating one or a series of electrical discharges in a liquid at a rise rate of the leading voltage front of at least 1010 V / s (energy is dosed by counting charges) 4) enhancement of the effect of destruction of microorganisms due to the formation of tension waves when compression waves formed by an electric discharge are reflected from the free surface of the liquid 5) suppression or suppression of shock waves in the inlet and outlet fluid lines to prevent their destruction6) removal of disinfected fluid from the working volume.
14 slide
Description of the slide:
Disinfection by ultrasound The advantage of using ultrasound over many other means of disinfection of wastewater is its insensitivity to factors such as high turbidity and color of water, the nature and number of microorganisms, as well as the presence of dissolved substances in water. The only factor that affects the effectiveness of ultrasonic disinfection of wastewater is the intensity of ultrasonic vibrations. Ultrasound is sound vibrations, the frequency of which is much higher than the level of audibility. The frequency of ultrasound is from 20,000 to 1,000,000 Hz, which results in its ability to have a detrimental effect on the state of microorganisms. Bactericidal action ultrasound of different frequencies is very significant and depends on the intensity of sound vibrations. Disinfection and purification of water by ultrasound is considered one of the latest methods disinfection. Ultrasonic impact on potentially dangerous microorganisms is not often used in drinking water filters, but its high efficiency suggests that this method of water disinfection is promising, despite its high cost.
15 slide
Description of the slide:
Radiation disinfection There are proposals to use gamma radiation for water disinfection. RHUND-type gamma-ray plants operate according to the following scheme: water enters the cavity of the mesh cylinder of the receiving-separating apparatus, where solid inclusions are carried upwards by the screw, squeezed out in the diffuser and sent to the bunker-collector. Then the water is diluted with conditionally pure water to a certain concentration and fed into the apparatus of the gamma-installation, in which, under the action of gamma radiation of the Co60 isotope, the disinfection process takes place. Gamma radiation has a depressing effect on the activity of microbial dehydrases (enzymes). At high doses of gamma radiation, most of the pathogens of such dangerous diseases as typhoid, poliomyelitis, etc., die.
16 slide
Description of the slide:
Conclusion Protection water resources from depletion and pollution and their rational use for the needs National economy is one of the most important problems requiring urgent solutions. Enterprises that take water from water sources and purify it, in terms of the level of tasks to be solved and the turnover of funds, occupy one of the leading places in the region. And therefore, the efficiency of the use of material resources in a given industry in one way or another affects general level well-being and health of the people living in the area. Rational, i.e. organized in compliance with sanitary rules and regulations, drinking water supply helps to avoid various epidemics, intestinal infections. Chemical composition Drinking water is also important for human health.
17 slide
Description of the slide:
18 slide
Description of the slide:
With the help of various filtration methods, mechanical suspensions and dissolved substances are removed from the water. It is softened, freed from organic and inorganic compounds. However, after filtration, biological contaminants may remain in the water. Not every filter can handle bacteria and viruses, many of which cause human diseases. To eliminate biological contamination, drinking water is disinfected.
A number of methods are used for disinfection. All of them are divided into three main groups: physical, chemical and combined.
This group includes methods in which chemical reagents are used. The liquid is treated with chlorine-containing substances or chlorine, ozone and some other compounds that affect biological objects. When using chemicals, it is important to accurately determine the amount of reagent and exposure time. Substances in small doses can not always kill all bacteria, some remain and quickly restore their numbers.
It is also impossible to increase the dose more than necessary. Many substances are toxic and can cause poisoning if consumed by humans. In addition, they form mutagenic and carcinogenic compounds.
Chlorination
A common method of water treatment is chlorination. This is an old method that remains popular to this day. The popularity is explained by the cheapness of the components, efficiency, long aftereffect, due to which there is no re-growth of microorganisms.
However, chlorine is highly toxic, it creates mutagenic and carcinogenic compounds. Far from always they are kept by filters. Only very fine purification allows you to free water from such components.
Rice. 1 Purification and disinfection of water with chlorineTrihalomethane compounds, which are highly carcinogenic, cause the greatest harm to humans. Chlorine and derivatives can cause diseases of the digestive system, heart and blood vessels, as well as some others.
To disinfect water, bleach is used, directly chlorine itself and other compounds.
Ozonation
When ozone is added to water, it decomposes into atomic oxygen, which has a strong oxidizing activity. It destroys microbial cell systems, eliminates a number of odors. But with excessive application, ozone itself creates an unpleasant odor and enhances corrosion processes, which destroys metal pipes.
This method is one of the safest for human health. Its small distribution is explained by high costs and complexity. The use of ozonation requires special complex equipment and specialists who can work with it. With this method of disinfection, energy consumption increases.
Rice. 2 Method of purification and disinfection of water with ozone Ozone itself is toxic and in some cases explosive. For private households, this method of disinfection will be very costly. It will require not only an expensive installation, but also regular visits to a specialist to maintain the system.
Other reagents
The group of other reagents is very extensive. It includes polymer antiseptics that are effective and do not harm the human body. This also includes compounds of heavy metals, bromine and iodine. They are not used often, because they require accurate calculations and certain knowledge, but their use allows you to effectively purify water from bacterial contamination.
Rice. 3 Home disinfection method Disinfect water and strong oxidizing agents. These include sodium hypochlorite, potassium permanganate, hydrogen peroxide and some others. When using them, it is necessary to correctly calculate the dose, and in the case of potassium permanganate, also remove manganese compounds.
Physical methods of disinfection
Physical methods are based on the use of ultraviolet rays, ultrasound and other methods that kill microorganisms. The water is pre-purified from suspension, since turbidity reduces the effectiveness of the impact.
UV disinfection
Ultraviolet rays have an effect on the metabolism in the bacterial cell and on its enzyme systems. Bacterial spores are also destroyed. At the same time, the taste, color and smell of water do not change. Toxic substances are not formed when exposed, so you can increase the dose of radiation.
Rice. 4 To disinfect water with ultraviolet light, you need an installation To perform ultraviolet disinfection, a special installation is required. Its cost will be higher than the cost of chlorination, but cheaper than ozonation.
Use ultraviolet light only after water purification from mechanical suspensions. Turbidity prevents the penetration of rays.
The efficiency of the installation is reduced when mineral salts are deposited on the surface of the lamp. They are cleaned mechanically or by creating an acidic environment for the passing liquid.
Ultrasonic processing
The use of ultrasound for water disinfection is a relatively new technique. Sound waves with a certain frequency create voids in the water with a large difference in pressure. This pressure breaks the membranes of bacterial cells.
The nature of the bactericidal effect and the effectiveness of disinfection depends on the characteristics of sound vibrations. Their intensity plays a special role.
This treatment is safe for humans. It does not change the characteristics of water, but requires expensive equipment. The equipment needs to be serviced periodically, and the services of specialists are also not cheap.
Ultrasound is generated by a special generator. It can be piezoelectric or magnetostrictive.
When using ultrasound to kill microorganisms, it should be remembered that the low frequency of sound enhances the growth of bacteria. It is very important to set up the device correctly.
Boiling
The simplest option for physical disinfection is boiling. With its help, all types of microorganisms are destroyed. In addition to them, when boiling, antibiotics, dissolved gases are removed from the water and hardness is reduced.
Rice. 5 Cleansing by boiling Wide industrial application of this method of disinfection is impossible due to its high energy consumption.
Combined methods of disinfection
To increase the efficiency of water disinfection, the methods are used in combination. Usually non-reagent methods are combined with reagent ones.
An example of such an effect is the combination of ultraviolet treatment followed by chlorination. Ultraviolet kills all possible bacteria, viruses and their spores, and chlorination prevents re-infection. As a result, not only water is not contaminated with microorganisms for a long time, but also the amount of reagents used is significantly reduced. As the chlorine concentration decreases, so does negative impact on the human body.
There are other options for combined disinfection. So water is exposed to two physical methods at once: ultrasound and ultraviolet. The output is a completely disinfected volume of liquid. There are devices that combine these two methods.
Whichever option is chosen, a preliminary analysis of biological contamination is required. Based on this, the dosage of reagents, the duration of exposure and the need for additional purification are selected. At home, ultraviolet settings will be optimal.
Plan
Introduction.
1. Hygienic problems of drinking water disinfection.
2. Reagent (chemical) methods of drinking water disinfection.
2.1 Chlorination.
2.1.2 Chlorine dioxide.
2.1.3 Sodium hypochlorite.
2.2 Ozonation.
2.3 Other reagent methods of water disinfection.
3. Physical methods of drinking water disinfection.
3.1 Boiling.
3.2 Ultraviolet irradiation.
3.3 Electropulse method.
3.4 Ultrasonic disinfection.
3.5 Radiation disinfection.
3.6 Other physical methods.
4. Complex disinfection.
Conclusion.
Bibliography.
Introduction
Among the many branches of modern technology aimed at improving the standard of living of people, the improvement of populated areas and the development of industry, water supply occupies a large and honorable place. After all, water is an indispensable part of all living organisms, the vital activity of which is impossible without water. For the normal course of physiological processes in the human body and for the creation of favorable living conditions for people, the hygienic value of water is very important. At present, providing the population with high quality water has become a real problem.
The problem of drinking water supply affects many aspects of the life of human society throughout the history of its existence. At present, this is a social, political, medical, geographical, as well as engineering and economic problem. About 5-6% of the total water consumption is spent on drinking and domestic needs of the population, communal facilities, medical institutions, as well as on the technological needs of food industry enterprises. Technically, it is not difficult to supply such an amount of water, but the needs must be satisfied with water of a certain quality, the so-called drinking water.
Drinking water is water that meets the established regulatory requirements in terms of its quality in its natural state or after treatment (purification, disinfection) and is intended for drinking and domestic needs of a person. Basic requirements for the quality of drinking water: to be safe in epidemic and radiation terms, to be harmless in chemical composition, to have favorable organoleptic properties. To meet these requirements, a whole range of measures for the preparation of drinking water is currently used.
Of course, in rivers and other bodies of water there is a natural process of water self-purification. However, it proceeds very slowly. Rivers have long been unable to cope with wastewater discharges and other sources of pollution. But the level of bactericidal effects in wastewater often exceeds the norm by thousands and millions of times. Effluent enters rivers and lakes, and most city water utilities take their water from them. Thus, the mandatory processes in the preparation of drinking water are high-quality purification and disinfection of wastewater.
Disinfection of water is the process of destroying microorganisms present there. In the process of primary water treatment, up to 98% of bacteria are retained. But among the remaining bacteria, as well as among viruses, there may be pathogenic (disease-causing) microbes, for the destruction of which special water treatment is needed - its disinfection.
When completely treating surface water, disinfection is always necessary, and when using groundwater, only when the microbiological properties of the source water require it. But in practice, the use of both groundwater and surface water for drinking is almost always impossible without disinfection.
The water of natural sources of drinking water supply, as a rule, does not meet the hygienic requirements for drinking water and requires preparation before being supplied to the population - cleaning and disinfection.
Water purification, including its clarification and discoloration, is the first stage in the preparation of drinking water. As a result, suspended solids, helminth eggs and a significant part of microorganisms are removed from the water. But some pathogenic bacteria and viruses penetrate through treatment facilities and are contained in filtered water. To create a reliable and manageable barrier to the possible transmission of intestinal infections and other equally dangerous diseases through water, water disinfection is used, i.e. destruction of living and virulent pathogenic microorganisms - bacteria and viruses. After all, it is the microbiological contamination of water that occupies the first place in assessing the degree of risk to human health. Today it has been proven that the risk of diseases from pathogenic microorganisms present in water is thousands of times higher than when water is polluted with chemical compounds of various nature. Therefore, disinfection to the limits that meet the established hygienic standards is a prerequisite for obtaining drinking water.
In the practice of municipal water supply, reagent (chlorination, ozonation, exposure to silver preparations), non-reagent (ultraviolet rays, exposure to pulsed electrical discharges, gamma rays, etc.) and combined methods of water disinfection are used. In the first case, the desired effect is achieved by introducing biologically active compounds into the water. chemical compounds. Reagent-free disinfection methods involve the treatment of water by physical influences. And in combined methods, chemical and physical effects are used simultaneously.
When choosing a method of disinfection, one should take into account the danger to human health of residual amounts of biologically active substances used for disinfection or formed in the process of disinfection, the possibility of changing the physicochemical properties of water (for example, the formation of free radicals). Important characteristics of the disinfection method are also its effectiveness against various kinds micropopulation of water, dependence of the effect on environmental conditions.
With chemical methods of drinking water disinfection, in order to achieve a stable disinfecting effect, it is necessary to correctly determine the dose of the injected reagent and ensure a sufficient duration of its contact with water. The dose of the reagent is determined by trial disinfection or calculation methods. To maintain the desired effect in chemical methods of drinking water disinfection, the dose of the reagent is calculated with an excess (residual chlorine, residual ozone), which guarantees the destruction of microorganisms that enter the water for some time after disinfection.
With physical methods, it is necessary to bring to a unit volume of water a given amount of energy, defined as the product of the intensity of exposure (radiation power) by the contact time.
There are other restrictions in the use of one or another method of water disinfection. These limitations, as well as the advantages and disadvantages of disinfection methods, will be discussed in detail below.
2.1 Chlorination
The most common and proven method of water disinfection is primary chlorination. Currently, 98.6% of water is disinfected by this method. The reason for this is the increased efficiency of water disinfection and the efficiency of the technological process in comparison with other existing methods. Chlorination allows not only to purify water from unwanted organic and biological impurities, but also to completely remove dissolved salts of iron and manganese. Another major advantage of this method is its ability to ensure the microbiological safety of water during its transportation to the user due to the aftereffect.
A significant disadvantage of chlorination is the presence of free chlorine in the treated water, which worsens its organoleptic properties and causes the formation of side halogen-containing compounds (HCC). Most of the GSS are trihalomethanes (THM) - chloroform, dichlorobromomethane, dibromochloromethane and bromoform. Their formation is due to the interaction of active chlorine compounds with organic substances of natural origin. This process is extended in time up to several tens of hours, and the amount of THM formed, other things being equal, is the greater, the higher the pH of the water. To eliminate impurities, additional purification of water on coal filters is required. Currently, the maximum allowable concentrations for substances that are by-products of chlorination are set in various developed countries in the range from 0.06 to 0.2 mg/l and correspond to modern scientific ideas about the degree of their danger to health.
For chlorination of water, substances such as chlorine itself (liquid or gaseous), chlorine dioxide and other chlorine-containing substances are used.
2.1.1 Chlorine
Chlorine is the most common of all substances used to disinfect drinking water. This is due to the high efficiency, simplicity of the technological equipment used, the low cost of the reagent used - liquid or gaseous chlorine - and the relative ease of maintenance.
A very important and valuable quality of using chlorine is its aftereffect. If the amount of chlorine is taken with some calculated excess, so that after passing through the treatment plant, the water contains 0.3–0.5 mg / l of residual chlorine, then there is no secondary growth of microorganisms in the water.
However, chlorine is a potent toxic substance requiring special safety measures during its transportation, storage and use; measures to prevent catastrophic consequences in emergency situations. Therefore, there is a constant search for reagents that combine the positive qualities of chlorine and do not have its disadvantages.
Simultaneously with water disinfection, oxidation reactions of organic compounds occur, in which organochlorine compounds are formed in water, which are highly toxic, mutagenic and carcinogenic. Subsequent purification of water on active carbon cannot always remove these compounds. In addition to becoming a contaminant of drinking water, these highly persistent organochlorine compounds, when they pass through the water supply and sewage system, cause pollution of downstream rivers.
The presence of side compounds in water is one of the disadvantages of using gaseous as well as liquid chlorine (Cl2) as a disinfectant.
2.1.2 Chlorine dioxide
Currently, for the disinfection of drinking water, the use of chlorine dioxide (ClO2) is also proposed, which has several advantages, such as: a higher bactericidal and deodorizing effect, the absence of organochlorine compounds in the treatment products, improved organoleptic qualities of water, no need to transport liquid chlorine. However, chlorine dioxide is expensive and must be produced locally using rather complex technology. Its application is promising for installations of relatively small productivity.
The effect of ClO2 on the pathogenic flora is due not only to the high content of released chlorine during the reaction, but also to the resulting atomic oxygen. It is this combination that makes chlorine dioxide a stronger disinfectant. In addition, it does not impair the taste and smell of water. The limiting factor in the use of this disinfectant until recently was the increased explosiveness, which complicated its production, transportation and storage. However, modern technologies make it possible to eliminate this disadvantage by producing chlorine dioxide directly at the place of use.
2.1.3 Sodium hypochlorite
The technology for using sodium hypochlorite (NaClO) is based on its ability to decompose in water to form chlorine dioxide. The use of concentrated sodium hypochlorite reduces secondary pollution by a third compared to the use of gaseous chlorine. In addition, the transportation and storage of a concentrated NaClO solution is quite simple and does not require increased security measures. It is also possible to obtain sodium hypochlorite directly on site, by electrolysis. The electrolytic method is characterized by low costs and safety; the reagent is easily dosed, which allows you to automate the process of water disinfection.
2.1.4 Chlorine-containing preparations
The use of chlorine-containing reagents (bleach, sodium and calcium hypochlorites) for water disinfection is less dangerous to maintain and does not require complex technological solutions. True, the reagent economy used in this case is more cumbersome, which is associated with the need to store large quantities of preparations (3–5 times more than when using chlorine). The volume of traffic increases by the same amount. During storage, partial decomposition of the reagents occurs with a decrease in the chlorine content. There is still a need to install an exhaust ventilation system and observe safety measures for maintenance personnel. Solutions of chlorine-containing reagents are corrosive and require equipment and pipelines made of stainless materials or with an anti-corrosion coating.
Plants for the production of active chlorine-containing reagents by electrochemical methods are becoming more and more widespread, especially at small water treatment plants. In Russia, several enterprises offer installations such as "Saner", "Sanator", "Chlorel-200" for the production of sodium hypochlorite by the diaphragm electrolysis of common salt.
drinking water supply disinfection
2.2 Ozonation
The advantage of ozone (O3) over other disinfectants lies in its inherent disinfecting and oxidizing properties, due to the release of active atomic oxygen upon contact with organic objects, which destroys the enzyme systems of microbial cells and oxidizes some compounds that give water an unpleasant odor (for example, humic bases). In addition to the unique ability to kill bacteria, ozone is highly effective in killing spores, cysts and many other pathogenic microbes. Historically, the use of ozone began as early as 1898 in France, where pilot plants for the preparation of drinking water were first created.
The amount of ozone required for the disinfection of drinking water depends on the degree of water pollution and is 1–6 mg/l upon contact for 8–15 minutes; the amount of residual ozone should be no more than 0.3–0.5 mg/l, since a higher dose gives the water a specific odor and causes corrosion of water pipes.
From a hygienic point of view, water ozonation is one of the best ways to disinfect drinking water. With a high degree of water disinfection, it provides its best organoleptic characteristics and the absence of highly toxic and carcinogenic products in purified water.
Limitations for the spread of ozonation technology are the high cost of equipment, high power consumption, significant production costs, as well as the need for highly qualified equipment. The latter fact determined the use of ozone only for centralized water supply. In addition, during operation it was found that in a number of cases (if the temperature of the treated natural water exceeds 22 °C), ozonation does not allow achieving the required microbiological indicators due to the lack of the effect of prolonging the disinfecting effect.
The method of water ozonation is technically complex and the most expensive among other methods of drinking water disinfection. . All this limits the use of this method in everyday life.
Another significant disadvantage of ozonation is the toxicity of ozone. The maximum permissible content of this gas in the air of industrial premises is 0.1 g/m3. In addition, there is a danger of an explosion of the ozone-air mixture.
The existing designs of modern ozonizers are a large number of closely spaced cells formed by electrodes, one of which is under high voltage, and the second is grounded. An electric discharge occurs between the electrodes with a certain periodicity, as a result of which ozone is formed from the air in the zone of action of the cells. The resulting ozone-air mixture is bubbled through the treated water. Water prepared in this way is superior in taste, smell and other properties to water treated with chlorine.
2.3 Other reagent methods for water disinfection
The use of heavy metals (copper, silver, etc.) for the disinfection of drinking water is based on the use of their "oligodynamic" properties - the ability to have a bactericidal effect in low concentrations. These metals can be introduced in the form of salt solutions or by electrochemical dissolution. In both these cases, indirect control of their content in water is possible. It should be noted that MPCs of silver and copper ions in drinking water are quite strict, and the requirements for water discharged into fishery reservoirs are even higher.
Chemical methods for the disinfection of drinking water also include widely used in the early 20th century. disinfection with bromine and iodine compounds, which have more pronounced bactericidal properties than chlorine, but require more sophisticated technology. In modern practice, for the disinfection of drinking water by iodization, it is proposed to use special ion exchangers saturated with iodine. When water is passed through them, iodine is gradually washed out of the ion exchanger, providing the necessary dose in water. This solution is acceptable for small-sized individual installations. A significant disadvantage is the change in the concentration of iodine during operation and the lack of constant monitoring of its concentration.
The use of active carbons and cation exchangers saturated with silver, for example, C-100 Ag or C-150 Ag from Purolite, does not aim to “silver” the water, but to prevent the development of microorganisms when the flow of water stops. When stopping, ideal conditions are created for their reproduction - a large amount of organic matter retained on the surface of the particles, their huge area and elevated temperature. The presence of silver in the structure of these particles dramatically reduces the likelihood of contamination of the loading layer. Silver-containing cation exchangers developed by OAO NIIPM - KU-23SM and KU-23SP - contain a much larger amount of silver and are designed for water disinfection in small-capacity installations.
3.1 Boiling
Of the physical methods of water disinfection, the most common and reliable (in particular, at home) is boiling.
Boiling destroys most bacteria, viruses, bacteriophages, antibiotics and other biological objects, which are often found in open water sources, and as a result, in central water supply systems.
In addition, when water is boiled, gases dissolved in it are removed and hardness decreases. The taste qualities of water during boiling change little. True, for reliable disinfection, it is recommended to boil water for 15 - 20 minutes, because. during short-term boiling, some microorganisms, their spores, helminth eggs can remain viable (especially if microorganisms are adsorbed on solid particles). However, the use of boiling on an industrial scale, of course, is not possible due to the high cost of the method.
3.2 Ultraviolet radiation
UV treatment is a promising industrial method for water disinfection. In this case, light with a wavelength of 254 nm (or close to it), which is called bactericidal, is used. The disinfecting properties of such light are due to their action on cellular metabolism and especially on the enzyme systems of the bacterial cell. At the same time, bactericidal light destroys not only vegetative, but also spore forms of bacteria.
Modern UV disinfection units have a capacity from 1 to 50,000 m3 / h and are a stainless steel chamber with UV lamps placed inside, protected from contact with water by transparent quartz covers. Water, passing through the disinfection chamber, is continuously exposed to ultraviolet radiation, which kills all microorganisms in it. The greatest effect of disinfection of drinking water is achieved when UV installations are located after all other purification systems, as close as possible to the place of final consumption.
This method is acceptable both as an alternative and as an addition to traditional disinfectants, since it is absolutely safe and effective.
It is important to note that, unlike oxidative methods, no secondary toxins are formed with UV irradiation, and therefore there is no upper threshold for the dose of ultraviolet irradiation. Increasing the dose will almost always achieve the desired level of decontamination.
In addition, UV irradiation does not impair the organoleptic properties of water, so it can be classified as an environmentally friendly method of water treatment.
However, this method also has certain disadvantages. Like ozonation, UV treatment does not provide a long-lasting effect. It is the absence of an aftereffect that makes its use problematic in cases where the time interval between the impact on water and its consumption is sufficiently large, for example, in the case of centralized water supply. For individual water supply, UV installations are the most attractive.
In addition, reactivation of microorganisms and even the development of new strains resistant to radiation damage are possible.
This method requires the strictest adherence to technology,
The organization of the process of UV disinfection requires more capital investments than chlorination, but less than ozonation. Lower operating costs make UV disinfection and chlorination economically comparable. Energy consumption is negligible, and the cost of annual lamp replacement is no more than 10% of the installation price.
A factor that reduces the efficiency of UV disinfection units during long-term operation is the contamination of quartz lamp covers with deposits of organic and mineral composition. Large installations are equipped with an automatic cleaning system that performs washing by circulating water through the installation with the addition of food acids. In other cases, mechanical cleaning is used.
Another factor that reduces the effectiveness of UV disinfection is the turbidity of the source water. Scattering of rays significantly impairs the efficiency of water treatment.
3.3 Electric pulse method
A fairly new method of water disinfection is the electropulse method - the use of impulsive electrical discharges (IED).
The essence of the method lies in the occurrence of an electro-hydraulic shock, the so-called effect of L. A. Yutkin.
The technological process consists of six steps:
liquid supply to the working volume with a uniform speed distribution profile (moreover, the working volume is filled with an air gap, and a uniform liquid distribution profile helps to reduce the energy intensity of the process),
charging the energy storage device in constant power mode,
initiation of one or a series of electrical discharges in a liquid at a rate of rise of the leading edge of the voltage of at least 1010 V / s (energy is dosed by counting charges),
enhancement of the effect of destruction of microorganisms due to the formation of tension waves during the reflection of compression waves formed by an electric discharge from the free surface of the liquid,
suppression or damping of shock waves in the inlet and outlet lines to prevent their destruction,
removal of disinfected liquid from the working volume.
In addition, in a particular case, it is possible to initiate electric discharges in a volume separated from the working volume by a medium that maintains or increases the amplitude of compression waves. An example of a material that is a medium that preserves the wave amplitude at the boundary with water is polystyrene foam.
In the process of disinfecting drinking water by electropulse, a large number of phenomena occur: powerful hydraulic processes, the formation of ultra-high pressure shock waves, the formation of ozone, cavitation phenomena, intense ultrasonic vibrations, the occurrence of impulsive magnetic and electric fields, and an increase in temperature. The result of all these phenomena is the destruction of almost all pathogenic microorganisms in water. It is very important to note that water treated with IES acquires bactericidal properties that last up to 4 months.
The main advantage of the electropulse method of drinking water disinfection is environmental friendliness, as well as the possibility of using large volumes of liquid.
However, this method has a number of disadvantages, in particular, a relatively high energy consumption (0.2-1 kWh/m3) and, as a result, high cost.
electrochemical method.
The "Emerald", "Sapphire", "Aquamin" installations, etc. are serially produced. Their work is based on the passage of water through an electrochemical diaphragm reactor, divided by an ultrafiltration ceramic-metal membrane into the cathode and anode regions. When applying direct current in the cathode and anode chambers, the formation of alkaline and acidic solutions, the electrolytic formation of active chlorine occurs. In these environments, almost all microorganisms perish and partial destruction of organic contaminants occurs. The design of a flow-through electrochemical element is well developed, and a set of a different number of such elements is used to obtain installations of a given capacity.
3.4 Ultrasonic disinfection
In some cases, ultrasound is used to disinfect water. This method was first proposed in 1928. The mechanism of action of ultrasound is not completely clear. In this regard, the following assumptions are made:
Ultrasound causes the formation of voids in a highly swirling space, which leads to a rupture of the bacterial cell wall;
Ultrasound causes the release of gas dissolved in the liquid, and gas bubbles in the bacterial cell cause it to burst.
The advantage of using ultrasound over many other means of wastewater disinfection is its insensitivity to factors such as high turbidity and color of water, the nature and number of microorganisms, and the presence of dissolved substances in water.
The only factor that affects the effectiveness of ultrasonic disinfection of wastewater is the intensity of ultrasonic vibrations. Ultrasound is sound vibrations, the frequency of which is much higher than the level of audibility. The frequency of ultrasound is from 20,000 to 1,000,000 Hz, which results in its ability to have a detrimental effect on the state of microorganisms. The bactericidal effect of ultrasound of different frequencies is very significant and depends on the intensity of sound vibrations.
Disinfection and purification of water by ultrasound is considered one of the latest methods of disinfection. Ultrasonic impact on potentially dangerous microorganisms is not often used in drinking water filters, but its high efficiency suggests that this method of water disinfection is promising, despite its high cost.
3.5 Radiation decontamination
There are proposals to use gamma radiation for water disinfection.
RHUND-type gamma-ray plants operate according to the following scheme: water enters the cavity of the mesh cylinder of the receiving-separating apparatus, where solid inclusions are carried upwards by the screw, squeezed out in the diffuser and sent to the bunker-collector. Then the water is diluted with conditionally pure water to a certain concentration and fed into the apparatus of the gamma-installation, in which, under the action of gamma radiation of the Co60 isotope, the disinfection process takes place.
Gamma radiation has a depressing effect on the activity of microbial dehydrases (enzymes). At high doses of gamma radiation, most of the pathogens of such dangerous diseases as typhoid, poliomyelitis, etc., die.
3.6 Other physical methods
Physicochemical methods of water disinfection include the use of ion-exchange resins for this purpose. G. Gillissen (1960) showed the ability of anion-exchange resins to release liquid from bacteria of the coli group. Resin regeneration is possible. Here, E.V. Shtannikov (1965) established the possibility of purifying water from viruses with ion-exchange polymers. According to the author, this effect is associated with both the sorption of the virus and its denaturation due to an acidic or especially alkaline reaction. In another work by Shtannikov, the possibility of disinfecting water with ion-active polymers, where the botulinum toxin is located, is pointed out. Disinfection occurs due to the oxidation of the toxin and its sorption.
In addition to the above physical factors, the possibility of disinfecting water with high-frequency currents and magnetic treatment was studied.
In many cases, the most effective is the complex use of reagent and non-reagent methods of water disinfection. The combination of UV disinfection with subsequent chlorination in small doses provides both the highest degree of purification and the absence of secondary biocontamination of water. Thus, the treatment of pool water with UV irradiation in combination with chlorination achieves not only a high degree of disinfection, a decrease in the threshold concentration of chlorine in water, but also, as a result, significant savings in chlorine consumption and an improvement in the situation in the pool itself.
Similarly, the use of ozonation is spreading, in which the microflora and part of the organic pollution are destroyed, followed by gentle chlorination, which ensures the absence of secondary biocontamination of water. At the same time, the formation of toxic organochlorine substances is sharply reduced.
Since all microorganisms are characterized by a certain size, passing water through a filter partition with pore sizes smaller than microorganisms can completely purify water from them. So, filter elements with a pore size of less than 1 micron, according to the current TI 10-5031536-73-10 for non-alcoholic products, are considered sterilizing, i.e. sterilizing. Although only bacteria are removed from the water, not viruses. For more “fine” processes, when the presence of any microorganisms is unacceptable, for example, in microelectronics, filters with pores no larger than 0.1–0.2 μm are used.
Conclusion
Protection of water resources from depletion and pollution and their rational use for the needs of the national economy is one of the most important problems requiring urgent solutions.
Enterprises that take water from water sources and purify it, in terms of the level of tasks to be solved and the turnover of funds, occupy one of the leading places in the region. And therefore, the efficiency of the use of material resources in this industry in one way or another affects the general level of well-being and health of people living in a given territory. Rational, i.e. organized in compliance with sanitary rules and regulations, drinking water supply helps to avoid various epidemics, intestinal infections. The chemical composition of drinking water is also important for human health.
In modern conditions, disinfection has become almost the only mandatory process in a multi-stage water purification system for drinking water supply. Coagulation and filtration of water through sand release it from suspended impurities and partially reduce its bacterial contamination. But only water disinfection can purify water from pathogenic (pathogenic) microorganisms by 98%.
The constant improvement of the methods and means by which disinfection is carried out is caused by two factors: the development of resistance in microorganisms not only to antibiotics, but also to disinfectants, as well as the imperfection of the disinfectants used. It should also be taken into account that secondary contamination of already prepared water is possible during its transportation through the pipes of the distribution network.
In this regard, the search and implementation of the most rational way of water disinfection is moving from an urgent problem to a socially significant one.
Continuous improvement of disinfectants will lead to the creation of new, effective and safe compounds. New disinfectants are already being developed based on such traditional groups of chemical compounds as alcohols, aldehydes, phenols, peroxides, surfactants and chlorine-containing substances. In addition, the possibility of combining them to create a composite disinfectant is constantly being developed.
Disinfection is the final stage in the preparation of drinking water and should ensure the epidemiological safety of the population.
Drinking water is an essential factor for human health and well-being.
World and domestic experience proves that when using advanced technologies and equipment, water quality (virtually regardless of its initial characteristics) begins to meet the most stringent regulatory requirements. This allows not only the efficient use of natural sources, but also the successful application of recycling schemes. Such an approach will undoubtedly help to reduce the anthropogenic load from environment and save it for posterity.
The problem of water disinfection is all the more acute today, since its quality in natural sources is steadily deteriorating. The state report "Drinking Water" notes that about 70% of the country's rivers and lakes have lost their quality as sources of water supply, and approximately 30% of underground sources have been subjected to natural or anthropogenic pollution. About 22% of drinking water samples taken from water pipes do not meet hygienic requirements for sanitary and chemical standards, and more than 12% - for microbiological indicators.
Bibliography
1. Water supply. Design of systems and structures: In 3 volumes - V. 2. Cleaning and conditioning natural waters/ Scientific and methodological guide and general editor doc. tech. sciences, prof. Zhurby M.G. Vologda-Moscow: VoGTU, 2001. - 324 p.
2. Mazaev V.T., Korlev A.A., Shlepnina T.G. Communal hygiene / Ed. V.T. Mazaev. - 2nd ed., Rev. and additional - M.: GEOTAR-Media, 2005. - 304 p.
3. Yakovlev S.V., Voronov Yu.V. Water disposal and wastewater treatment / Textbook for universities: - M .: DIA, 2002 - 704 p.
Currently, the problem of water disinfection is very relevant, so this topic was chosen as an individual task. Also, the choice of the topic of an individual task was influenced by its direct relation to the topic of my master's work.
Water disinfection is an activity during which microorganisms and viruses that cause infectious diseases are destroyed.
According to the method of influencing microorganisms, water disinfection methods are divided into thermal (boiling); oligodynamic (treatment with noble metal ions); physical (disinfection with ultraviolet rays, ultrasound, etc.); chemical (treatment with oxidizing agents: chlorine and its compounds, ozone, potassium permanganate, etc.).
thermal method
Boiling is an exclusively domestic method of disinfection, but it does not fully guarantee the death of bacteria or their spores. In addition, when boiling, the gases dissolved in it (oxygen, carbon dioxide) are removed from the water, which reduces its taste properties.
When boiling, a partial softening of water occurs due to the fact that part of the calcium and magnesium salts precipitate, which turn from soluble hydrocarbonate salts into insoluble carbonate ones.
Water disinfection with silver
Water treatment, which contains 0.05 - 0.2 mg / dm 3 silver, for 30 - 60 minutes makes it possible to achieve sanitary norms. To dissolve silver in water, methods are used to contact water with a developed metal surface, by dissolving silver salts, or by electrolytically dissolving metallic silver. The most widespread is the last method based on the anodic dissolution of silver.
However, silver, like other heavy metals, can accumulate in the body and cause disease (argyrosis - silver poisoning). In addition, for the bactericidal effect of silver on bacteria, sufficiently high concentrations are required, and in acceptable amounts (about 50 µg/l), it can only have a bacteriostatic effect, i.e. stop the growth of bacteria without killing them. And some types of bacteria are practically not sensitive to silver at all.
All these properties limit the use of silver. It may be appropriate only for the purpose of preserving the original clean water for long term storage.
Disinfection of water with ultraviolet rays
This method is based on the ability of ultraviolet radiation with a certain wavelength to have a detrimental effect on the enzyme systems of bacteria. Ultraviolet rays destroy not only vegetative, but also spore forms of bacteria, and do not change the organoleptic properties of water. It is important to note that since UV irradiation does not form toxic products, there is no upper dose threshold. By increasing the dose of UV radiation, the desired level of disinfection can almost always be achieved. Mercury lamps made of quartz sand are used as a radiation source.
& nbsp & nbsp & nbsp & nbsp & nbsp metro does not require complex equipment and can easily be used in household water treatment complexes in private houses.
& nbsp & nbsp & nbsp & nbsp & nbsp factor, which reduces the efficiency of operations of UV recovery during prolonged operation, is pollution of the quartz covers of lamps with organic and mineral deposits. Large installations are equipped with an automatic cleaning system that performs washing by circulating water through the installation with the addition of food acids. In other cases, mechanical cleaning is used.
The main disadvantage of the method is the complete absence of aftereffect.
Ultrasonic water treatment
Disinfection of water by ultrasound is based on its ability to cause so-called cavitation - the formation of voids that create a large pressure difference, which leads to rupture cell wall and death of the bacterial cell. The bactericidal effect of ultrasound of different frequencies is very significant and depends on the intensity of sound vibrations.
At present, this method has not yet found sufficient application in water purification systems, although in medicine it is widely used for disinfection of instruments, etc. in so-called ultrasonic cleaners.
Ozonation
Water ozonation is based on the property of ozone to decompose in water with the formation of atomic oxygen, which destroys the enzyme systems of microbial cells and oxidizes some compounds that give the water an unpleasant odor (for example, humic bases). The amount of ozone required for water disinfection depends on the degree of water pollution and is 1–6 mg/dm 3 upon contact for 8–15 minutes; the amount of residual ozone should be no more than 0.3–0.5 mg/dm 3 , since a higher dose gives the water a specific odor and causes corrosion of water pipes. 
However, the ozone molecule is unstable, so its residual amounts quickly decompose in water. From a hygienic point of view, water ozonation is one of the best ways to disinfect drinking water. With a high degree of water disinfection, it provides its best organoleptic characteristics and the absence of highly toxic and carcinogenic products in purified water.
However, due to the high consumption of electricity, the use of complex equipment and the need for highly qualified service, ozonation has found application for the disinfection of drinking water only with centralized water supply.
The water ozonation method is technically complicated and the most expensive. The technological process includes successive stages of air purification, its cooling and drying, ozone synthesis, mixing of the ozone-air mixture with treated water, removal and destruction of the residual ozone-air mixture, and its release into the atmosphere. All this also requires additional auxiliary equipment (ozonizers, compressors, air dryers, refrigeration units, etc.), bulk construction and installation works.
Ozone is toxic. The maximum permissible content of this gas in the air of industrial premises is 0.1 g/m3. In addition, there is a danger of an explosion of the ozone-air mixture.
Chlorination
The most common method of water disinfection has been and remains the method of chlorination. This is due to the high efficiency, simplicity of the technological equipment used, the low cost of the reagent used - liquid or gaseous chlorine - and the relative ease of maintenance.
A very important and valuable quality of the chlorination method is its aftereffect. If the amount of chlorine is taken with some calculated excess, so that after passing through the treatment plant, the water contains 0.3–0.5 mg / l of residual chlorine, then there is no secondary growth of microorganisms in the water.
& nbsp & nbsp & nbsp & nbsp & nbsphlor is a potent toxic substance requiring special safety measures for its transportation, storage and use; measures to prevent catastrophic consequences in emergency situations. Therefore, there is a constant search for reagents that combine the positive qualities of chlorine and do not have its disadvantages.
The use of chlorine dioxide is proposed, which has a number of advantages, such as: a higher bactericidal and deodorizing effect, the absence of organochlorine compounds in the processing products, an improvement in the organoleptic qualities of water, and no need to transport liquid chlorine. However, chlorine dioxide is expensive and must be produced locally using a rather complex technology. Its application is promising for installations of relatively small productivity.
The use of chlorine-containing reagents (bleach, sodium and calcium hypochlorites) for water disinfection is less dangerous to maintain and does not require complex technological solutions. However, the reagent economy used in this case is more cumbersome, which is associated with the need to store large quantities of preparations (3–5 times more than when using chlorine). The volume of traffic increases by the same amount. During storage, partial decomposition of the reagents occurs with a decrease in the chlorine content. There is still a need to install an exhaust ventilation system and observe safety measures for maintenance personnel. Solutions of chlorine-containing reagents are corrosive and require equipment and pipelines made of stainless materials or with an anti-corrosion coating.
